Bash shell stores history of the commands you execute, and you can inspect this history using the history command.

But if you do not want your session history to be saved (maybe you are doing something nasty, which you don't want others to know about), you can use the above command to disable the history logging feature for your session, and nobody will know what you did.

PS: There are other audit trails which can still incriminate you, so don't smugly assume that the above command makes you an invisible hacker.

I use them to create self-signed certificates for my Postgres
installations.

For the purposes of Postgres connections, you need to replace CN=example with CN=actual-database-user-name in the command titled 'Create a signed certificate for the client'. Then place the
server.* and root.* files in the Postgres' data directory. Place the
client.* and root.crt files on the client machine and use the following
format to connect, say psql utility, to the database: